The present invention relates generally to a light guide structure, and more particularly to a light guide strip structure composed of a transparent main body and a color band embedded in the main body. The light is refracted and reflected between the main body and the color band and scattered from the surface of the main body to create neon effect.
A conventional light guide generally includes a transparent core body and a protective layer or a thin sleeve coated on the surface of the core body. The core body is made of a thermoplastic plastic material such as PC, PU, Ethyl, Methyl Acrylate or the like polymer material. The protective layer or sleeve is made of PE material. For example, U.S. Pat. No. 4,422,719, entitled “optical distribution system including light guide”, discloses a combination of transparent core body and a semitransparent sleeve. The sleeve has a refractive index greater than that of the core body to enhance light reflection and elongate the travel distance of the light within the core body as well as uniform and soften the scattered or diffused light. However, the sleeve will blur the scattered light and deteriorate the brightness. This is proved from the product of the above patent.
There is another factor causing the vagueness of the scattered light. That is, the inner surface of the sleeve and the surface of the core body are very close to each other. It is very possible that the light ray reflected from one of the surfaces is interfered with and offset by the light ray reflected from the other of the surfaces. For example, in case that the light source projects white light and the thickness of the sleeve is relatively thin, the blue light in the white light is apt to be offset due to interference. Therefore, the light reflected to the eyes will become yellow light (complementary color to blue) with less brightness. When the thickness of the sleeve is increased, the green light in the white light is apt to be offset and a color complementary to green will appear. In other words, due to interference, the brightness of such light guide structure, in which the core body is coated with the sleeve, will be deteriorated.
To overcome this problem, U.S. Pat. No. 4,422,719 provides some other embodiments. For example, the sleeve and the core body are notched with marks arranged at different intervals. Alternatively, a photosensitive emulsion, reflective powder material or metal oxide is added into the sleeve for enhancing the brightness. However, this makes it more complicated to manufacture the light guide structure.
U.S. Pat. No. 6,169,836 B1 entitled “optical transmission tube and method for making the same” and U.S. Pat. No. 7,433,565 B2 entitled “side-scattering light guides” disclose light guide structures with core bodies and protective layers or sleeves coated on the core bodies. In the above patents, the refractive index of the core body is greater than the refractive index of the sleeve. However, the protective layer or the sleeve also will blur the scattered light and deteriorate the brightness and visual effect. This is also proved from their products.
In order to increase the brightness of the light guide structure, the core body is doped with light-scattering particles or diffuser particles made of organic polymers (such as silicone resin, PS resin, metal oxide, carbonate or the like material) for enhancing reflection and refraction of light. As known by those skilled in this field, it is relatively complicated to manufacture such light guide structure with the light-scattering particles or diffuser particles. This is because after the light-scattering particles are added into the resolved and polymerized core body, it is necessary to further distribute the light-scattering particles over the interior of the core body by means of vibration and rotation operation. The cost for such process is reflected on the price. Therefore, the price of a 20 cm long light guide strip is very high, up to 70˜80 NT$.
There is another topic about the application of the light-scattering particles or diffuser particles to the light guide structure. That is, when the light projected into the core body encounters the light-scattering particles or diffuser particles, a shadow is often formed behind the light-scattering particles or diffuser particles to produce diffraction stripes on the edges of the shadow. In some cases, the diffraction stripes will mix with each other to blur the edges of the shadow. The diffraction extent is determined by the relationship between the sizes of the light-scattering particles or diffuser particles and the wavelength of the light. (For example, the longer the wavelength is, the more obvious the diffraction is.) Accordingly, only limited varieties of light sources are applicable to the light guide structure. This is unexpected.
U.S. Pat. No. 7,433,565 B2 discloses another embodiment in which an air layer or a medium layer is disposed between the core body and the sleeve. The air layer or medium layer has a refractive index smaller than that of the core body. In this case, the core body is spaced from the sleeve by the air layer so that the light rays will be respectively reflected from the upper and lower faces of the air layer. The reflected light rays will interfere with each other to produce alternate bright and dark stripes. This is because the light rays are reflected to the eyes respectively from the inner surface of the sleeve and the outer surface of the core body in different paths. The light ray reflected from the outer surface of the core body needs to travel through a longer distance to reach an observer's eyes. In the case that the distance difference is just half the wavelength (out of phase), offset interference will take place to produce dark band. In the case that the distance difference is such that no interference takes place, bright band is produced. That is, the light ray reflected from the inner surface of the sleeve and the outer surface of the core body, which is very close to the inner surface of the sleeve, will interfere with each other to produce interference stripes and reduce the brightness of the light rays.
It is therefore tried by the applicant to provide a light guide strip structure, in which the bright-and-dark stripes and diffraction existing in the prior art are minimized and the problem of interference between the light rays is improved to enhance the brightness. Also, the problem of vagueness existing in the prior art is overcome. The light guide strip structure has the following advantages:    1. In contrast to the above the patents (U.S. Pat. Nos. 4,422,719, 6,169,836 B1 and 7,433,565 B2), the surface of the main body of the light guide strip structure is not coated with any protective layer or sleeve structure. Therefore, the vagueness or unclearness existing in the prior art can be minimized.    2. In contrast to U.S. Pat. Nos. 4,422,719, 6,169,836 B1 and U.S. Pat. No. 7,433,565 B2, the main body of the light guide strip structure is free from any light-scattering particle or diffuser particle so that the shadow or diffraction stripes are minimized. In this case, various light sources can be used without limitation. Also, the light guide strip can be manufactured at lower cost with less complicatedness.    3. The internal structure of the light guide strip is rearranged and redesigned to keep or enhance reflection and refraction of light.    4. The areas of the surfaces (such as the inner surface of the sleeve and the surface of the core body), which are very close to each other, are as reduced as possible. Accordingly, the offset and interference between the light rays reflected by the two surfaces or the bright-and-dark stripes are minimized.